Book I. DISEASES OF VEGETABLES. 261 



Willdenow describes it as occasioning a preternatural swelling of particular parts, and 

 inducing putrefaction. It is said to take place chiefly in bulbous and tuberous roots, 

 which are often found much swelled after rain. It affects fruits also, which it renders 

 watery and insipid. It prevents the ripening of seeds, and occasions an immoderate pro- 

 duction of roots from the stem. 



1633. Succulent plants. This disease generally appears in consequence of excessive waterings, and is 

 generally incurable. The leaves drop, even though plump and green ; and the fruit rots before reaching 

 V maturity. In this case the absorption seems to be too great in proportion to the transpiration ; but the 

 soil when too much manured produces similar effects. l)u Hamel planted some elms in a soil that was 

 particularly well manured, and accordingly they pushed with great vigor for some time ; but at the end of 

 live or six years they all died suddenly. The bark was found to be detached from the wood, and the cavity 

 filled up with a reddish-colored water. The symptoms of this disease suggest the palliatives ; and the pre- 

 ventive is ever the same judicious culture. 



1664. Fhix of juices. Some trees, but particularly the oak and birch, are liable to a 

 great loss of sap either bursting out spontaneously, owing to a superabundance of sap, or 

 issuing from accidental wounds; sometimes it is injurious to the health of the plant, and 

 sometimes not. 



1665. There is a spontaneous extravasation of the sap of the vine, known by the name of the tears of the 

 vine, which is not always injurious. As it often happens that the root imbibes sap, which the leaves are 

 not yet prepared to throw off, because not yet sufficiently expanded, owing to an inclement season, the sap 

 which is first carried up, being propelled by that which follows, ultimately forces its way through all ob- 

 structions, and exudes from the bud. But this is observed only in cold climates ; for in hot climates where 

 the developement of the leaves is not obstructed by cold, they are ready to elaborate the sap as soon as it 

 reaches them. There is also a spontaneous extravasation of proper juice in some trees, which does not 

 seem in general to be injurious to the individual. Thus the gum which exudes from cherry, plum, peach, 

 and almond trees, is seldom detrimental to their health, except when it insinuates itself into the other 

 vessels of the plant and occasions obstructions. 



1666. But the exudation of gum is sometimes a disease, and one for which there is seldom any remedy. 

 It is generally the consequence of an unsuitable soil, situation, or climate. Cold raw summers will pro- 

 duce it in the peach, apricot, and more under-sorts of plum and cherry ; or grafting these fruits on diseased 

 stocks. Cutting out the part and applying a covering of loam or tar and charcoal to exclude the air are 

 palliatives ; but the only effectual method, where it can be practised, is to take up the tree and place it in 

 a suitable soil and situation. 



. 1667. The extravasation and corruption of the ascending or descending juices, has been known to occa- 

 sion a fissure of the solid parts. Sometimes the fissure is occasioned by means of frost, forming what is 

 called a double alburnum ; that is, first a layer that has been injured by the frost, and then a layer that 

 passes into wood. Sometimes a layer is partially affected, and that is generally owing to a sudden and 

 partial thaw on the south side of the trunk, which may be followed again by a sudden frost. In this case 

 the alburnum is split into clefts or chinks, by means of the expansion of the frozen sap. 



1668. ChUldains. But clefts thus occasioned often degenerate into chilblains that discharge a blackish 

 and acrid fluid to the great detriment of the plant, particularly if the sores are so situated that rain or snow 

 will readily lodge in them, and become putrid. The same injury may be occasioned by the bite or punc- 

 ture of insects while the shoot is yet tender ; and as no vegetable iilcer heals up of its own accord, the 

 sooner a cure is attempted the better, as it will, if left to itself, ultimately corrode and destroy the whole 

 plant, bark, wood, and pith. The only palliative is the excision of the part affected, and the application of 

 acoat of grafting wax. {Willdenow, p. 354.) 



1669. Gangrene. Of this disorder there are two varieties, the dry and the wet. The 

 former is occasioned by means of excessive heat or excessive cold. If by means of cold, 

 it attacks the leaves of young shoots and causes them to shrink up, converting them from 

 green to black ; as also the inner bark, which it blackens in the same manner, so that it 

 is impossible to save the plant except by cutting it to the ground. If by means of heat, 

 the effects are nearly simflar, as may oftentimes be seen in gardens, or even in forests, 

 where the foresters are allowed to clear away the moss and withered leaves from the 

 roots. Sometimes the disease is occasioned by the too rapid growth of a particular 

 branch, depriving the one that is next it of its due nourishment, and hence inducing its 

 decay. Sometimes it is occasioned by means of parasitical plants, as in the case of the 

 bulbs of the saffron, which a species of lycoperdon often attaches itself to and totally 

 corrupts. 



1670. Dry gangrene. The harmattan winds of the coast of Africa kill many plants, by means of 

 inducing a sort of gangrene that withers and blackens the leaves, and finally destroys the whole plant. 

 The nopal of Mexico is also subject to a sort of gangrene that begins with a black spot, and extends 

 till the whole leaf or branch rots oft", or the plant dies. But plants are .sometimes affected with a 

 gangrene by which a part becomes first soft and moist, and then dissolves into foul ichor. This is confined 

 chiefly to the leaves, flowers, and fruit. Sometimes it attacks the roots also, but rarely the stem. It 

 seems to be owing, in many cases, to too wet or too rich a soil ; but it may originate in contusion, and may 

 be caught by infection. But the nopal is subject also to a disease calletl by Thierv, la dissolution con- 

 sidered by Sir J. E. Smith as distinct from gangrene, and which appears to be Willdenow's dry gangrene 

 A joint o'f the noi)al, or a whole branch, and sometimes an entire plant, changes in the space of a single 

 hour, from a state of apparent health to a state of putrefaction or dissolution. Now its surface is verdant 

 and shining, and in an instant it changes to a yellow, and its brilUancy is gone. If the substance is cut 

 into, the parts are found to have lost all cohesion, and are quite rotten ; the attempt at a cure is by speedy 

 amputation below the diseased part. Sometimes the vita! i)rinciple collecting and exerting all its energies 

 makes a stand as it were against the encroaching disease, and throws off the infected part. {Smith's Intro- 

 duction, p. 340.) 



1671. Etiolation. Plants are sometimes affected by a disease which entirely destroys 

 their verdure, and renders them pale and sickly. This is called etiolation, and may arise 

 merely from want of the agency of light, by which the extrication of oxygen is effected 

 and the leaf rendered green. And hence it is that plants placed in dark rooms, or be- 

 tween great masses of stone, or in the clefts of rocks, or utuler tlie shade of other trees, 



S :3 



